Ultrafast electronic relaxation of nucleobases from 1ππ* states to the ground state (S0) is considered essential for the photostability of DNA. However, transient absorption spectroscopy (TAS) has indicated that some nucleobases in aqueous solutions create long-lived 1nπ*/3ππ* dark states from the 1ππ* states with a high quantum yield of 0.4–0.5. We investigated electronic relaxation in pyrimidine nucleobases in both aqueous solutions and the gas phase using extreme ultraviolet (EUV) time-resolved photoelectron spectroscopy. Femtosecond EUV probe pulses cause ionization from all electronic states involved in the relaxation process, providing a clear overview of the electronic dynamics. The 1nπ* quantum yields for aqueous cytidine and uracil (Ura) derivatives were found to be considerably lower (<0.07) than previous estimates reported by TAS. On the other hand, aqueous thymine (Thy) and thymidine exhibited a longer 1ππ* lifetime and a higher quantum yield (0.12–0.22) for the 1nπ* state. A similar trend was found for isolated Thy and Ura in the gas phase: the 1ππ* lifetimes are 39 and 17 fs and the quantum yield for 1nπ* are 1.0 and 0.45 for Thy and Ura, respectively. The result indicates that single methylation to the C5 position hinders the out-of-plane deformation that drives the system to the conical intersection region between 1ππ* and S0, providing a large impact on the photophysics/photochemistry of a pyrimidine nucleobase. The significant reduction of 1nπ* yield in aqueous solution is ascribed to the destabilization of the 1nπ* state induced by hydrogen bonding.

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In this research, an InZnO channel layer and a high-k SrTa2O6 gate insulator were both fabricated using a solution process for the application of thin film transistors (TFTs). A low turn-on voltage of -1.2 V, a low threshold voltage of 0.8 V, a high on/off current ratio of 5×106 at a low voltage of 5 V, and a saturation mobility of 0.24 cm2/(V·s) were obtained. The diffusion of oxygen from the high-k SrTa2O6 gate insulator to the InZnO channel layer through the interface was effective for decreasing the concentration of impurities in solution-processed InZnO TFTs and subsequently enhancing mobility. Furthermore, a very low subthreshold swing value of 0.1 V/decade was obtained. This low value was due to the very smooth surface and the voltage-independent high dielectric constant of 36 for the SrTa2O6 thin film.

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The color sensitivity of a thin-film phototransistor using a polycrystalline-silicon film with a p/i/n structure has been evaluated. First, the illuminance and voltage dependences of the detected current for white, red, green, and blue light are measured. It is found that the photoinduced current is proportional to the illuminance and that the detected current is slightly dependent on the applied voltage. Next, the conversion efficiencies from the colored light to the photoinduced current are calculated. It is found that the illuminance efficiency is considerably different for the different colors, whereas the quantum efficiency is similar for the different colors. The quantum efficiency is on the order of 0.1 but lower for the red light and higher for the blue light. This suggests that the electron–hole pairs generated by the red light have lower energy and tend to be recombined and disappear, whereas those generated by the blue light have higher energy and tend to be separated and contribute to the photoinduced current. The color sensitivity must be considered when the thin-film phototransistor is used in actual photosensor applications.